When maintenance work is required on distribution cables, to protect the worker from accidental energization of the cable, the common industry practice is to ground the cable section at both terminals. However there are some drawbacks with such a safety procedure. First, some testing or maintenance procedures requires that the cable core be “floating” and do not permit the section of cable core in question to be grounded. Second, if a ground fault occurs, for example, at the substation, the rise in potential of the station ground will cause significant current to flow through the grounded cable sheath which, due to mutual coupling, induces voltage in the cable core. Simultaneously, the induced voltage in the core will force current to flow which is proportional to the closed circuit impedance formed by the cable core, terminal effective grounding impedances and the sheath conductor which is in parallel with the earth ground return. Therefore, any significant reduction of the terminal impedance by grounding an isolated cable core may cause dangerous current to flow through the worker. There is therefore a need for a safety device which protects a worker both from accidental energization and from ground fault when working on a distribution cable.